[PowerPC] VSX instruction latency corrections

The vector divide and sqrt instructions have high latencies, and the scalar
comparisons are like all of the others. On the P7, permutations take an extra
cycle over purely-simple vector ops.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205096 91177308-0d34-0410-b5e6-96231b3b80d8